OZONE AND METEOROLOGY DURING THE 1994 POLAR SUNRISE EXPERIMENT

Observations of ozone mixing ratios in the lower troposphere of Arctic Canada in April 1994 are summarized. Except during a brief period of anomalous transport from high altitude, air depleted in ozone was alwa ys observed above sea ice and snow throughout the northern Ellesmere I sland/Lincoln Sea region, or whenever air was sampled which had been i n recent contact with sea ice and snow. Ozone mixing ratios observed a t a camp on the sea ice north of Alert were consistent with a 1992 stu dy. Observations at the ice camp confirmed that ozone was depleted mor e frequently (74% of all observations <5 ppbv than at coastal and inla nd sites near Alert (10% of observations <5 ppbv). Mixing ratios brief ly attained a maximum of 36 ppbv at the ice camp but were normally com pletely depleted or below typical free tropospheric levels of 35-45 pp bv observed elsewhere in the region. Aircraft measurements and vertica l profiles of ozone and meteorological parameters from balloon sondes confirmed that ozone depletion existed in a layer above the sea ice, f rom the surface up to heights of 200-400 m. Some observations showed a very abrupt transition between depleted and nondepleted conditions at the upper boundary of the layer. The occurrence of a layer of fully d epleted ozone was well correlated with surface high-pressure systems. At Alert the appearance of ait that was fully depleted in ozone was dr iven by advection from ocean areas to the north. A fortuitous set of m eteorological conditions allowed the use of a simple model for testing general aspects of some proposed hypotheses for ozone destruction, du ring a period when it is believed the depleted layer was forming. It w as found that the observed rate of ozone destruction would require lev els of HO and Cl atoms much higher than would be expected for the prev ailing conditions but reasonable concentrations of Br atoms. It was al so found that an effective ozone deposition velocity of 0.1-0.2 cm s(- 1) could account for the observed depletion rate during this period. T hat is, the observed rate of ozone depiction during formation of a dep leted layer was consistent with either a volume sink or a surface sink for ozone.